diff --git a/Makefile.in b/Makefile.in
index d476189..3dc06ea 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -32,11 +32,13 @@ SOURCE=\
 	persistent-data/error_set.cc \
 	persistent-data/hex_dump.cc \
 	persistent-data/lock_tracker.cc \
+	persistent-data/transaction_manager.cc \
+	\
 	persistent-data/space_map.cc \
 	persistent-data/space-maps/disk.cc \
 	persistent-data/space-maps/recursive.cc \
 	persistent-data/space-maps/careful_alloc.cc \
-	persistent-data/transaction_manager.cc \
+	\
 	thin-provisioning/human_readable_format.cc \
 	thin-provisioning/metadata.cc \
 	thin-provisioning/metadata_checker.cc \
@@ -112,9 +114,9 @@ THIN_CHECK_SOURCE=\
 	persistent-data/hex_dump.cc \
 	persistent-data/lock_tracker.cc \
 	persistent-data/space_map.cc \
-	persistent-data/space_map_disk.cc \
-	persistent-data/space_map_recursive.cc \
-	persistent-data/space_map_careful_alloc.cc \
+	persistent-data/space-maps/disk.cc \
+	persistent-data/space-maps/recursive.cc \
+	persistent-data/space-maps/careful_alloc.cc \
 	persistent-data/transaction_manager.cc \
 	thin-provisioning/metadata.cc \
 	thin-provisioning/metadata_checker.cc \
diff --git a/persistent-data/array.h b/persistent-data/data-structures/array.h
similarity index 100%
rename from persistent-data/array.h
rename to persistent-data/data-structures/array.h
diff --git a/persistent-data/array.tcc b/persistent-data/data-structures/array.tcc
similarity index 100%
rename from persistent-data/array.tcc
rename to persistent-data/data-structures/array.tcc
diff --git a/persistent-data/btree.h b/persistent-data/data-structures/btree.h
similarity index 99%
rename from persistent-data/btree.h
rename to persistent-data/data-structures/btree.h
index b87e6a6..d20fb5c 100644
--- a/persistent-data/btree.h
+++ b/persistent-data/data-structures/btree.h
@@ -19,8 +19,8 @@
 #ifndef BTREE_H
 #define BTREE_H
 
-#include "endian_utils.h"
-#include "transaction_manager.h"
+#include "persistent-data/endian_utils.h"
+#include "persistent-data/transaction_manager.h"
 
 #include <boost/noncopyable.hpp>
 #include <boost/optional.hpp>
diff --git a/persistent-data/btree.tcc b/persistent-data/data-structures/btree.tcc
similarity index 99%
rename from persistent-data/btree.tcc
rename to persistent-data/data-structures/btree.tcc
index eb0584b..702b69b 100644
--- a/persistent-data/btree.tcc
+++ b/persistent-data/data-structures/btree.tcc
@@ -18,9 +18,9 @@
 
 #include "btree.h"
 
-#include "errors.h"
-#include "checksum.h"
-#include "transaction_manager.h"
+#include "persistent-data/errors.h"
+#include "persistent-data/checksum.h"
+#include "persistent-data/transaction_manager.h"
 
 #include <iostream>
 
diff --git a/persistent-data/btree_checker.h b/persistent-data/data-structures/btree_checker.h
similarity index 98%
rename from persistent-data/btree_checker.h
rename to persistent-data/data-structures/btree_checker.h
index 2b579ae..9ebe2e9 100644
--- a/persistent-data/btree_checker.h
+++ b/persistent-data/data-structures/btree_checker.h
@@ -19,10 +19,11 @@
 #ifndef BTREE_CHECKER_H
 #define BTREE_CHECKER_H
 
-#include "block_counter.h"
 #include "btree.h"
-#include "checksum.h"
-#include "error_set.h"
+
+#include "persistent-data/block_counter.h"
+#include "persistent-data/checksum.h"
+#include "persistent-data/error_set.h"
 
 #include <sstream>
 #include <map>
diff --git a/persistent-data/space-maps/disk.h b/persistent-data/space-maps/disk.h
index 636ab5f..070bc44 100644
--- a/persistent-data/space-maps/disk.h
+++ b/persistent-data/space-maps/disk.h
@@ -20,7 +20,7 @@
 #define SPACE_MAP_DISK_H
 
 // FIXME: why is btree_checker needed?
-#include "persistent-data/btree_checker.h"
+#include "persistent-data/data-structures/btree_checker.h"
 #include "persistent-data/space_map.h"
 
 //----------------------------------------------------------------
diff --git a/persistent-data/space-maps/disk_structures.h b/persistent-data/space-maps/disk_structures.h
index 9020c1f..99e7227 100644
--- a/persistent-data/space-maps/disk_structures.h
+++ b/persistent-data/space-maps/disk_structures.h
@@ -20,7 +20,9 @@
 #define SPACE_MAP_DISK_STRUCTURES_H
 
 #include "persistent-data/endian_utils.h"
-#include "persistent-data/btree.h"
+
+// FIXME: what's this included for?
+#include "persistent-data/data-structures/btree.h"
 
 //----------------------------------------------------------------
 
diff --git a/thin-provisioning/metadata.h b/thin-provisioning/metadata.h
index 1fc545a..564071f 100644
--- a/thin-provisioning/metadata.h
+++ b/thin-provisioning/metadata.h
@@ -20,7 +20,7 @@
 #define METADATA_LL_H
 
 #include "persistent-data/block.h"
-#include "persistent-data/btree.h"
+#include "persistent-data/data-structures/btree.h"
 #include "persistent-data/endian_utils.h"
 #include "persistent-data/space-maps/disk.h"
 #include "persistent-data/transaction_manager.h"
diff --git a/thin-provisioning/metadata_disk_structures.h b/thin-provisioning/metadata_disk_structures.h
index b5ccee1..77cb3dc 100644
--- a/thin-provisioning/metadata_disk_structures.h
+++ b/thin-provisioning/metadata_disk_structures.h
@@ -20,7 +20,7 @@
 #define METADATA_DISK_STRUCTURES_H
 
 #include "persistent-data/endian_utils.h"
-#include "persistent-data/btree.h"
+#include "persistent-data/data-structures/btree.h"
 
 //----------------------------------------------------------------
 
diff --git a/thin-provisioning/thin_debug.cc b/thin-provisioning/thin_debug.cc
index 4fb0f40..acfdc61 100644
--- a/thin-provisioning/thin_debug.cc
+++ b/thin-provisioning/thin_debug.cc
@@ -28,7 +28,7 @@
 #include <string>
 #include <vector>
 
-#include "persistent-data/btree.h"
+#include "persistent-data/data-structures/btree.h"
 #include "thin-provisioning/metadata.h"
 #include "thin-provisioning/metadata_checker.h"
 #include "version.h"
diff --git a/thin-provisioning/thin_pool.cc b/thin-provisioning/thin_pool.cc
index 25938d7..71716c2 100644
--- a/thin-provisioning/thin_pool.cc
+++ b/thin-provisioning/thin_pool.cc
@@ -18,7 +18,7 @@
 
 #include "thin-provisioning/thin_pool.h"
 
-#include "persistent-data/btree_checker.h"
+#include "persistent-data/data-structures/btree_checker.h"
 
 #include <stdexcept>
 #include <sstream>
diff --git a/unit-tests/btree_t.cc b/unit-tests/btree_t.cc
index c4daf2a..ff86dbb 100644
--- a/unit-tests/btree_t.cc
+++ b/unit-tests/btree_t.cc
@@ -18,7 +18,7 @@
 
 #include "persistent-data/transaction_manager.h"
 #include "persistent-data/space-maps/core.h"
-#include "persistent-data/btree.h"
+#include "persistent-data/data-structures/btree.h"
 
 #define BOOST_TEST_MODULE BTreeTests
 #include <boost/test/included/unit_test.hpp>